Safety control system for gaseous fuel burners



P. R. MARVIN Aug. 15, 1950 SAFETY CONTROL SYSTEM FOR GASEOUS FUEL BURNERS Filed Sept. 17, 1947 in/06%?" A39 7770/0172 lull Patented Aug. 15, 1950 SAFETY CONTROL SYSTEM FOR GASEOUS FUEL BURNERS Philip R. Marvin, Wauwatosa, Wis., assignor to Milwaukee Gas Specialty Company, Milwaukee, Wis., a corporation of Wisconsin Application September 17, 1947, Serial No. 774,497

'6 'Claims. 1

This invention relates, in general, to a burner control system, and is particularly concerned with controlling the operation of a burner so that it will be shut off in the event of the occurrence of an objectionable condition, such as a flash back or the like.

In the case of a gas burner, for example, the

gas is usually mixed with air in a mixing chamber adjacent to the burner, and the combustible mixture of gas and air is conducted to the burner where it is ignited by a pilot flame. At times the flame may flash back and the gaseous fuel will burn in the chamber where the mixture of air and gas normally takes place. Where such a flash back occurs, the gas often burns with insufficient oxygen, resulting in the production of a relatively large quantity of carbon monoxide which is highly objectionable and even dangerous, particularly in the absence of adequate flue connections.

One of the main objects of the present invention is to provide improved means which will operate automatically in the case of a flash back to shut off the supply of fuel to the burner.

Another object of the invention is to provide an improved flash back control in which prompt actuation of the valve in the fuel conduit to closed position upon the occurrence of a flash back condition is assured; also a system in which the valve in the fuel conduit is opened automatically and promptly when the pilot is ignited and no flash back condition exists.

Another object of the invention is to provide a flash back control system using thermistor type control means, and, more particularly, a combination of thermistor type devices for obtaining the improved form of control.

Another object of the invention is to provide in a burner control system having a first thermistor type of device subject to the heat of the pilot flame, the combination with such system of a second thermistor type of device responsive to the heat of a flash back condition and per able to disable the relay or other means for maintaining the valve open so that the valve will 0perate to closed position to shut oil the supply of fuel upon the occurrence of a flash back condigrid circuit of a vacuum tube.

Another object of the invention is to provide for automatically energizing the coil of a relay or like device for controlling the valve in the fuel supply conduit by means of a thermistor located in position where it will be subject to the heat of the pilot flame and connected in the cathode circuit of a vacuum tube.

Another object of the invention is to provide a burner control system of the character described having various features of novelty and advantages, and which is particularly characterized by its simplicity in construction, its economy in manufacture, its efiectiveness in use, and the absence of moving contacts and the like in the devices subjected to the heat of the pilot flame and to the heat of a flash back condition.

' Further objects and advantages of the invention will appear from the following detailed description, taken in connection with the accompanying drawing, in which the single figure is a diagram showing, schematically, the parts and circuit connections of one form of system embodying the present invention.

Referring now to the drawing, the burner shown at l is a main burner. It may be the main burner for a room or space heater, or it may be the burner for a water heater or for a floor furnace, an oven burner, one or more top burners for a gas range, or any other burner, and of any suitable construction.

A fuel supply pipe or conduit 2 leads tothe burner l for the delivery of gaseous or other fuel thereto, for example, through a mixing chamber 3 to which air is admitted through adjustable air inlets (not shown), as well understood in the art. The flow of gas through the conduit 2 is controlled by a valve 4 of any suitable electroresponsive or electrically operated type. For purposes of illustration, the valve 4 may be a solenoid valve operated to open position by the flow of electric current through its coil 6, and to closed position by a spring 1 or by gravity.

Interposed in the fuel supply pipe 2 anterior of valve 4 is a thermoelectric safety shutoff valve 8. The thermoelectric safety shutoff valve 8 is, in general, of the type shown and described in Clarence Wantz Patent No. 2,307,870, issued J anuary 12,1943. Suffice it to state that it comprises a valve body having an inlet at 9 for receiving gaseous or other fuel, and an outlet it] through which this fuel is delivered to the valve 4 and thence, when valve 4 is open, to the main burner. Contiguous sections of pipe 2 are connected to inlet 9 and outlet ID. A port or passage, shown more or less diagrammatically in dotted lines at.

also the flow of fuel for a pilot burner l3 located" in juxtaposition or in lighting proximity to the burner I.

An electromagnet, having a magnet frame l4 and a coil I5, is adapted for holding armature l3 connected to valve |2 in attracted position, and, thereby, the valve |2 open when the thermoelectric generator |'|such as a thermocouple or thermopileis heated by the pilot flame. When the pilot I3 is extinguished, the electromagnet, which is connected in circuit with the thermoelectric generator, ceases to hold the valve l2 open, and this valve moves to closed position, for example, under the action of a spring l8 to shut oil! the supply of fuel to burner I; also the supply of fuel to the pilot burner.

A reset button |3 is adapted to be pressed inwardly to move valve l2 to open position with accompanying movement of armature Hi to attracted position, and to hold the armature in attracted position until the pilot is ignited and heats the thermoelectric generator sufilciently to retain ar'mature l6 attracted and valve l2 open. A flow interrupter valve 20 shuts ofi the flow of fuel to the main burner during the resetting operation and until valve I2 is held in open position by the electromagnet and button I3 is released and returns to its outwardly projecting position with accompanying operation of the flow interrupter valve 2|] to open position. The details and mode of operation of a suitable reset and flow interrupter valve arrangement are shown and described in the above identified patent of Clarence Wantz: also in Charles V. Hildebrecht Patent No. 2,114,446. issued April 19, 1938.

The pipe 2| for supplying fuel to the pilot burner |3 may be connected, for example, as shown more or less diagrammatically at 22 to the interior of the body of the thermoelectric safety shutoff valve 8 between the above mentioned valve seats at opposite ends of the port or passage H. In this way, the valve I2, when in closed position, shuts off the supply of fuel to both th main burner I and pilot burner l3, and fuel flows to the pilot burner |3 whenever the valve I2 is open and regardless of whether the flow interrupter valve 20 is or is not open.

Electric power for operating the valve 4 is supplied from a suitable source, for example, from the line wires 23 of a suitable source of a] rnatlng current, such as a household current su 'ly line of the type which averages about 115 volts. Power for the operation of the valve 4 may be supplied by a transformer 24. This transformer comprises, for example, a high voltage primary 25 connected to the line wires 23, and a low voltage secondary 26, one side of which is connected by a conductor 21 to one side of coil 3. The other side of the secondary 26 is connected by a conductor 28 and through contacts 29 and 30 of a relay having acoil 3| to the other side of coil 6.

Power for relay coil 3| is supplied, for example, by a transformer 32 having a high voltage primary 33 connected to the line wires 23, and a low voltage secondary 34, one side of which is connected in circuit with the plate 35 of a vacuum tube 36 by a conductor 31.

A thermistor 38 is positioned so as to be heated by the flame of pilot burner l3 when the pilot flame is burning. The thermistor 38, which is 4. to the heat of the pilot flame or a corresponding \temperature, and changes to an electric conductor when heated by the pilot flame or a corresponding temperature.

One side of the thermistor 33 is connected in circuit with the cathode 33 of the tube 36 by a conductor 40. The other side of the thermistor 33 is connected to the other side of secondary 34 by a conductor 4| 'which includes a resistor 42 and relay coil 3| in series with thermistor 38.

A second thermistor 43 is located in the mixing chamber or venturi 3 of the main burner where it will be subject to the heat of a flash back condition in such mixing chamber or venturi 3. The second thermistor 43 has a negative temperature coefllcient of resistivity, i. e., it is a nonconductor, or relatively a non-conductor, when not subjected to the heat of a flash-back condition in the mixing chamber or venturi 3. One side of thermistor 43 is connected to the conductor 4| ahead of the coil 3| by a conductor 44. In the drawing the conductor 44 is shown connected to conductor 4| between resistor 42 and coil 3|. The other side of the thermistor 43 is connected to the secondary 34 at a mid point or intermediate position thereof by a conductor 45 which includes a resistor 46 in series with the thermistor 43. The conductor 44, thermistor 43, and conductor 45 constitute a bias circuit for vacuum tube 36 under control of thermistor 43. The conductors 44 and 45 may be led from the mixing chamber or venturi 3 through insulators 41. A conductor 48 is connected at one end to the conductor 45 at 49, and the opposite end of conductor 48 is connected in circuit with the grid 50 of tube 36.

In operation, cooking of the thermoelectric safety shut-off valve 8, by depressing the button l3, opens the valve l2, thus admitting gas to the pilot |3 which, when ignited, heats thermoelectric generator II and thereby maintains valve |2 in open position. In cocking or resetting the thermoelectric safety shut-off valve, the flow interrupter valve member 20 moves to closed position to shut off the flow of fuel to the main burner during the resetting operation and until the pilot I3 is ignited and heats thermoelectric generator sufllciently to hold valve I2 open. Then, upon release of button I9, valve member 26 moves to open position, admitting gas to solenoid valve 4.

Line voltage applied to primary 33 energizes secondary 34 which places voltage on the elepreferably not positioned directly in the flame ments of the vacuum tube 36 and results in a small current flow through the circuit comprising conductor 31, vacuum tube 33, conductor 40, thermistor 38, conductor 4|, resistor 42, and relay coil 3|. Flow of this small current through thermistor 38 and resistor 42 produces a negative bias on vacuum tube 36, which decreases when thermistor 38 is heated. This causes vacuum tube 36 to conduct heavily, which energizes relay coil 3| sufliciently to cause it to close relay contacts 23, 30 which applies power supplied by secondary 26 to solenoid valve 4, thereby opening valve 4 for admission of gas to the main burner I.

In case a flash back condition occurs, the thermistor 43 becomes heated. This decreases the positive bias on tube 36, thus deenergizing relay coil 3| sufllciently so that contacts 29 and 30 open. This opening or separation of contacts 23, 33 opens the circuit for the valve 4 which operates to closed position to shut off the supply of fuel to the main burner If, with the pilot l3 ignited and heating the M thermoelectric generator and valves 4, l2 and 20 open, the pilot flame is extinguished, the valve I2 moves to closed position to shut ofi the supply of fuel to both the main burner I and pilot I3. While it is preferable that the valve l2 be operable to shut off the supply of fuel to both the main burner and the pilot to assure 100% safety shutoff when the pilot is extinguished, it is to be understood that this may vary within the broader aspects of the present invention. It is to be further understood that a single primary may be employed for both secondaries 26 and 34 instead of providing a primary for each secondary. as shown and described, and that other variations from the particular system shown in the draw-' ing are contemplated within the scope of the present invention.

The embodiment of the invention shown in the drawing is for illustrative purposes only, and it is to be expressly understood that said drawing and the accompanying specification are not to be construed as a definition of the limits or scope of the invention, reference being had to the appended claims for that purpose.

I claim:

1. In a burner control system, a pilot burner, a main burner adjacent thereto and ignitable therefrom, electrically operated means for effecting supply of fuel to said main burner, a source of electric current, a circuit for energizing said fuel supply means from said source, said circuit including relay contacts for opening and closing said circuit, a second circuit including the plate, cathode and the conductive space of an electron tube having a grid, a first resistor having a negative coefiicient of resistivity positioned to be subjected to the heat of the pilot flame and connected into said second circuit, a relay coil connected into said second circuit in series with said first resistor and positioned in proximity to said relay contacts to close said contacts and thereby said first circuit when said first resistor is heated by the pilot flame, and a second resistor having a negative coeflicient of resistivitypositioned to be subjected to the heat of -a flash-back condition at the burner and connected to, said I grid whereby to suppress the conductivity of said first circuit through said tube space to a value to deenergize said relay coil sufilciently to permit said relay contacts to open and shut off the electrically operated means for eifecting supply of fuel to the main burner.

2. A system according to claim 1 wherein there are a pair of resistors having positive coefficients of resistivity, one connected in circuit with each of said first and second resistors.

3. In a burner control system, a pilot burner, a main burner adjacent thereto and ignitable therefrom, electrically operated means for effecting supply of fuel to said main burner, a source of electric current, a circuit for energizing said fuel supply means from said source, said circuit including relay contacts for opening and closing said circuit, a second circuit including the plate, cathode and the conductive space of an electron tube, a resistor having a negative coefficient of resistivity positioned to be subjected to the heat of the pilot flame and connected into said second circuit, and a relay coil connected into said second circuit in series with said first resistor and positioned in proximity to said relay contacts to close said contacts and thereby said first circuit when said resistor is heated by the pilot flame.

4. A system according to claim 3 wherein there is a second resistor having a negative coefiicient of resistivity positionedto be subjected to the heat of a flash-back condition at the burner, one side of said second resistor being connected in the grid circuit of the electron tube and the other side of said second resistor being connected to said second circuit.

5. In a burner control system, a pilot burner, a main burner adjacent thereto and ignitable therefrom, electrically operated means for eflecting supply of fuel to said main burner, a source of electric current, a circuit for energizing said fuel supply means from said source, said circuit including relay contacts for opening and closing said circuit, a second circuit including the plate, cathode and the conductive space of an electron tube having a grid, a first resistor having a negative coeflicient of resistivity positioned to be subjected to the heat of the pilot flame and connected into said second circuit, a relay coil connected into said second circuit in series with said first resistor and positioned in proximity to said relay contacts to close said contacts and thereby said first circuit when said first resistor is heated by the pilot flame, and a second resistor having a negative coefiicient of resistivity positioned to be subjected to the heat of a flash-back condition at the burner, one side of said second resistor being connected to the grid of the electron tube and the other side of said second resistor being connected to said second circuit, the plate of the electron tube being connected to said source of electric current and the cathode of said tube being connected to said first resistor.

6. In a system of the class described, in combination, a source of electric current, a first circult having relay contacts therein for opening and closing said circuit, a second circuit including the plate, cathode, and the conductive space of an electron tube having a grid, a first resistor having a negative coefiicient of resistivity positioned to be subjected to the heat of a flame and connected into said second circuit, a relay coil connected into said second circuit in series with said first resistor and positioned in proximity to said relay contacts to close said contacts and thereby said first circuit when said first resistor is heated by the flame, and a second resistor having a negative coefiicient Of resistivity positioned to be subjected to heat at a position remote from said first resistor and connected to said grid whereby to suppress the conductivity of said first circuit through said tube space to a value to deenergize said relay coil sufiiciently to permit said relay contacts to open when said second resistor is heated to a predetermined temperature.

PHILIP R. MARVlN.

REFERENCES crrap The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,858,265 Dahlstrom May 17, 1932 2,130,175 Betz et al Sept. 13, 1938 2,137,199 Betz Nov. 15, 1938 2,295,885 Yates Sept. 15, 1942 2,304,641 Jones Dec. 8, 1942 2,327,690 Ackerman Aug. 24, 1943 2,351,277 Mantz June 13, 1944 2,373,326 Miller Apr. 10, 1945 2,430,373 Strobel Nov. 4, 1947 

